How to achieve a similar effect (rocks)?
You could do it this way:


Create a plane, subdivide, play with the Fractal value in the Operator box, flatten it on the Z axis.





Extrude to create the cliff, extrude again to create a cliff on the cliff, create some horizontal edge loops:





Enable the Proportional Editing option and move some vertices. Don't give any Subsurf modifier or Smooth Shading to keep a low-poly look: